vendredi 13 avril 2012

In this image, the NASA/ESA Hubble Space Telescope has captured the brilliance of the compact center of Messier 70, a globular cluster. Quarters are always tight in globular clusters, where the mutual hold of gravity binds together hundreds of thousands of stars in a small region of space. Having this many shining stars piled on top of one another from our perspective makes globular clusters a popular target for amateur skywatchers and scientists alike.

Messier 70 offers a special case because it has undergone what is known as a core collapse. In these clusters, even more stars squeeze into the object's core than on average, such that the brightness of the cluster increases steadily towards its center.

The legions of stars in a globular cluster orbit about a shared center of gravity. Some stars maintain relatively circular orbits, while others loop out into the cluster's fringes. As the stars interact with each other over time, lighter stars tend to pick up speed and migrate out toward the cluster's edges, while the heavier stars slow and congregate in orbits toward the center. This huddling effect produces the denser, brighter centers characteristic of core-collapsed clusters. About a fifth of the more than 150 globular clusters in the Milky Way have undergone a core collapse.

Although many globular clusters call the galaxy's edges home, Messier 70 orbits close to the Milky Way's center, around 30 000 light-years away from the Solar System. It is remarkable that Messier 70 has held together so well, given the strong gravitational pull of the Milky Way's hub.

Messier 70 is only about 68 light-years in diameter and can be seen, albeit very faintly, with binoculars in dark skies in the constellation of Sagittarius (The Archer). French astronomer Charles Messier documented the object in 1780 as the seventieth entry in his famous astronomical catalogue.

This picture was obtained with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. The field of view is around 3.3 by 3.3 arcminutes.

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

A new observatory still under construction has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable clues about how such systems form and evolve. Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that planets orbiting the star Fomalhaut must be much smaller than originally thought. This is the first published science result from ALMA in its first period of open observations for astronomers worldwide.

The discovery was made possible by exceptionally sharp ALMA images of a disc, or ring, of dust orbiting Fomalhaut, which lies about 25 light-years from Earth. It helps resolve a controversy among earlier observers of the system. The ALMA images show that both the inner and outer edges of the thin, dusty disc have very sharp edges. That fact, combined with computer simulations, led the scientists to conclude that the dust particles in the disc are kept within the disc by the gravitational effect of two planets — one closer to the star than the disc and one more distant [1].

The bright star Fomalhaut in the constellation of Piscis Austrinus

Their calculations also indicated the probable size of the planets — larger than Mars but no larger than a few times the size of the Earth. This is much smaller than astronomers had previously thought. In 2008, a NASA/ESA Hubble Space Telescope image had revealed the inner planet, then thought to be larger than Saturn, the second largest planet in our Solar System. However, later observations with infrared telescopes failed to detect the planet.

That failure led some astronomers to doubt the existence of the planet in the Hubble image. Also, the Hubble visible-light image detected very small dust grains that are pushed outward by the star's radiation, thus blurring the structure of the dusty disc. The ALMA observations, at wavelengths longer than those of visible light, traced larger dust grains — about 1 millimetre in diameter — that are not moved by the star's radiation. They clearly reveal the disc's sharp edges and ringlike structure, which indicate the gravitational effect of two planets.

Wide-field view of the sky around the bright star Fomalhaut

"Combining ALMA observations of the ring's shape with computer models, we can place very tight limits on the mass and orbit of any planet near the ring," said Aaron Boley (a Sagan Fellow at the University of Florida, USA) who was leader of the study. "The masses of these planets must be small; otherwise the planets would destroy the ring," he added. The small sizes of the planets explain why the earlier infrared observations failed to detect them, the scientists said.

The ALMA research shows that the ring's width is about 16 times the distance from the Sun to the Earth, and is only one-seventh as thick as it is wide. "The ring is even more narrow and thinner than previously thought," said Matthew Payne, also of the University of Florida.

The ring is about 140 times the Sun-Earth distance from the star. In our own Solar System, Pluto is about 40 times more distant from the Sun than the Earth. "Because of the small size of the planets near this ring and their large distance from their host star, they are among the coldest planets yet found orbiting a normal star," added Aaron Boley.

Planets shepherding material into a narrow ring around Fomalhaut

The scientists observed the Fomalhaut system in September and October of 2011, when only about a quarter of ALMA's planned 66 antennas were available. When construction is completed next year, the full system will be much more capable. Even in this Early Science phase, though, ALMA was powerful enough to reveal the telltale structure that had eluded earlier millimetre-wave observers.

"ALMA may be still under construction, but it is already the most powerful telescope of its kind. This is just the beginning of an exciting new era in the study of discs and planet formation around other stars", concludes ESO astronomer and team member Bill Dent (ALMA, Chile).

Zooming in on Fomalhaut and its dusty disc

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Notes:

[1] The effect of planets or moons in keeping a dust ring's edges sharp was first seen when the Voyager spacecraft flew by Saturn and made detailed images of that planet's ring system. In another example in our Solar System, one ring of the planet Uranus is confined sharply by the moons Cordelia and Ophelia, in exactly the manner the ALMA observers propose for the ring around Fomalhaut. The moons confining those planets' rings are dubbed "shepherding moons".

The moons or planets confining such dust rings do so through gravitational effects. A planet on the inside of the ring is orbiting the star more rapidly than the dust particles in the ring. Its gravity adds energy to the particles, pushing them outward. A planet on the ring's outside is moving more slowly than the dust particles, and its gravity decreases the energy of the particles, making them fall slightly inward.

More information:

This research was presented in a paper, “Constraining the Planetary System of Fomalhaut Using High-Resolution ALMA Observations” by A. Boley et al. to appear in Astrophysical Journal Letters.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matter through a violent collision between two galaxy clusters.

Finding another system that is further along in its evolution than the Bullet Cluster gives scientists valuable insight into a different phase of how galaxy clusters -- the largest known objects held together by gravity -- grow and change after major collisions.

Researchers used observations from NASA's Chandra X-ray Observatory and Hubble Space Telescope as well as the Keck, Subaru and Kitt Peak Mayall telescopes to show that hot, X-ray bright gas in the Musket Ball Cluster has been clearly separated from dark matter and galaxies.

In this composite image, the hot gas observed with Chandra is colored red, and the galaxies in the optical image from Hubble appear as mostly white and yellow. The location of the majority of the matter in the cluster (dominated by dark matter) is colored blue. When the red and the blue regions overlap, the result is purple as seen in the image. The matter distribution is determined by using data from Subaru, Hubble and the Mayall telescope that reveal the effects of gravitational lensing, an effect predicted by Einstein where large masses can distort the light from distant objects.

In addition to the Bullet Cluster, five other similar examples of merging clusters with separation between normal and dark matter and varying levels of complexity, have previously been found. In these six systems, the collision is estimated to have occurred between 170 million and 250 million years earlier.

In the Musket Ball Cluster, the system is observed about 700 million years after the collision. Taking into account the uncertainties in the age estimate, the merger that has formed the Musket Ball Cluster is two to five times further along than in previously observed systems. Also, the relative speed of the two clusters that collided to form the Musket Ball cluster was lower than most of the other Bullet Cluster-like objects.

The special environment of galaxy clusters, including the effects of frequent collisions with other clusters or groups of galaxies and the presence of large amounts of hot, intergalactic gas, is likely to play an important role in the evolution of their member galaxies. However, it is still unclear whether cluster mergers trigger star formation, suppress it, or have little immediate effect. The Musket Ball Cluster holds promise for deciding between these alternatives.

The Musket Ball Cluster also allows an independent study of whether dark matter can interact with itself. This information is important for narrowing down the type of particle that may be responsible for dark matter. No evidence is reported for self-interaction in the Musket Ball Cluster, consistent with the results for the Bullet Cluster and the other similar clusters.

The Musket Ball Cluster is located about 5.2 billion light years away from Earth. A paper describing these results was led by Will Dawson from University of California, Davis and was published in the March 10, 2012 issue of The Astrophysical Journal Letters. The other co-authors were David Wittman, M. James Jee and Perry Gee from UC Davis, Jack Hughes from Rutgers University in NJ, J. Anthony Tyson, Samuel Schmidt, Paul Thorman and Marusa Bradac from UC Davis, Satoshi Miyazaki from the Graduate University for Advanced Studies (GUAS) in Tokyo, Japan, Brian Lemaux from UC Davis, Yousuke Utsumi from GUAS and Vera Margoniner from California State University, Sacramento.

Reliable Internet access on the Moon, near Mars or for astronauts on a space station? How about controlling a planetary rover from a spacecraft in deep space? These are just some of the pioneering technologies that ESA is working on for future exploration missions.

What do observation or navigation satellites orbiting Earth have in common with astronauts sending images in real time from the International Space Station? They all need to send data back home. And the complexity of sharing information across space is set to grow.

Networking in space: Mars Express

In the future, rovers on Mars or inhabited bases on the Moon will be supported by orbiting satellite fleets providing data relay and navigation services. Astronauts will fly to asteroids, hundreds of millions of kilometres from Earth, and they’ll need to link up with other astronauts, control centres and sophisticated systems on their vessels.

All of these activities will need to be interconnected, networked and managed.

Supporting future exploration

“We are researching how today’s technical standards for devices like mobile phones, laptops and portable computers can be applied to a new generation of networked space hardware,” says Nestor Peccia, responsible for ground segment software development at ESA’s Operations Centre in Darmstadt, Germany.

N. Peccia

“But our future focus goes well beyond just networking; we’re looking at how agencies like ESA and NASA cooperate in orbit and how to interchange data in real time between different organisations’ spacecraft and ground stations, as well as reliable technical standards for spacecraft navigation and flight control.”

Open technical standards through cooperation

Since 1982, experts from ESA, NASA and other major space organisations and industry have met periodically to develop new, open data communication standards as part of the Consultative Committee for Space Data Systems.

Developing standards for space hardware and data interchange for space agencies, commercial spaceflight companies and satellite manufacturers promises to pay off even in the short term.

In the future, inter-satellite communication requirements are predicted to grow, and spacecraft should be capable of establishing powerful radio links with each other – even while orbiting Mars at thousands of kilometres per hour.

In May 2008, ESA’s Mars Express served as a crucial data relay node for NASA’s Phoenix lander during descent and landing on the Red planet. Mars Express is set to repeat the feat in August with NASA’s Mars Science Laboratory.

ESOC - About the European Space Operations Centre

In December 2011, ESA’s worldwide tracking station network was recruited to provide three hours’ daily data contact for Russian mission controllers operating the Phobos–Grunt mission en route to Mars (the probe failed soon after launch for unrelated reasons).

Astronaut–machine interfaces at Mars

In October, ESA astronaut André Kuipers on the International Space Station will practise remotely controlling a test rover located at ESA’s Operations Centre to simulate orbiter–rover communication links at a planet like Mars.

“Setting technical standards and communication system architecture isn’t the most high-profile part of space exploration, but it’s absolutely vital for ensuring that the high-profile efforts – like sending an astronaut to Mars – will work as planned when that time comes,” says Nestor.

These and other topics are set to be discussed at the CCSDS conference in Darmstadt on 16–19 April, which will bring together international space organisations from 20 spacefaring nations including ESA, NASA, ASI, CNES, Roscosmos, DLR and JAXA.

jeudi 12 avril 2012

This artist's concept shows a "feeding," or active, supermassive black hole with a jet streaming outward at nearly the speed of light. Image credit: NASA/JPL-Caltech.

Astronomers are actively hunting a class of supermassive black holes throughout the universe called blazars thanks to data collected by NASA's Wide-field Infrared Survey Explorer (WISE). The mission has revealed more than 200 blazars and has the potential to find thousands more.

Blazars are among the most energetic objects in the universe. They consist of supermassive black holes actively "feeding," or pulling matter onto them, at the cores of giant galaxies. As the matter is dragged toward the supermassive hole, some of the energy is released in the form of jets traveling at nearly the speed of light. Blazars are unique because their jets are pointed directly at us.

"Blazars are extremely rare because it's not too often that a supermassive black hole's jet happens to point towards Earth," said Francesco Massaro of the Kavli Institute for Particle Astrophysics and Cosmology near Palo Alto, Calif., and principal investigator of the research, published in a series of papers in the Astrophysical Journal. "We came up with a crazy idea to use WISE's infrared observations, which are typically associated with lower-energy phenomena, to spot high-energy blazars, and it worked better than we hoped."

The findings ultimately will help researchers understand the extreme physics behind super-fast jets and the evolution of supermassive black holes in the early universe.

WISE surveyed the entire celestial sky in infrared light in 2010, creating a catalog of hundreds of millions of objects of all types. Its first batch of data was released to the larger astronomy community in April 2011 and the full-sky data were released last month.

Massaro and his team used the first batch of data, covering more than one-half the sky, to test their idea that WISE could identify blazars. Astronomers often use infrared data to look for the weak heat signatures of cooler objects. Blazars are not cool; they are scorching hot and glow with the highest-energy type of light, called gamma rays. However, they also give off a specific infrared signature when particles in their jets are accelerated to almost the speed of light.

One of the reasons the team wants to find new blazars is to help identify mysterious spots in the sky sizzling with high-energy gamma rays, many of which are suspected to be blazars. NASA's Fermi mission has identified hundreds of these spots, but other telescopes are needed to narrow in on the source of the gamma rays.

Sifting through the early WISE catalog, the astronomers looked for the infrared signatures of blazars at the locations of more than 300 gamma-ray sources that remain mysterious. The researchers were able to show that a little more than half of the sources are most likely blazars.

"This is a significant step toward unveiling the mystery of the many bright gamma-ray sources that are still of unknown origin," said Raffaele D'Abrusco, a co-author of the papers from Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. "WISE's infrared vision is actually helping us understand what's happening in the gamma-ray sky."

The team also used WISE images to identify more than 50 additional blazar candidates and observed more than 1,000 previously discovered blazars. According to Massaro, the new technique, when applied directly to WISE's full-sky catalog, has the potential to uncover thousands more.

This image taken by NASA's Wide-field Infrared Survey Explorer (WISE) shows a blazar -- a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed right toward Earth. Image credit: NASA/JPL-Caltech/Kavli.

"We had no idea when we were building WISE that it would turn out to yield a blazar gold mine," said Peter Eisenhardt, WISE project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is not associated with the new studies. "That's the beauty of an all-sky survey. You can explore the nature of just about any phenomenon in the universe."

The Kavli Institute for Particle Astrophysics and Cosmology is a joint institute of Stanford University and SLAC National Accelerator Laboratory in Menlo Park, Calif.

JPL manages and operates WISE for NASA's Science Mission Directorate in Washington. The principal investigator for WISE, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program, managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing and archiving take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Image above: A physicist monitors beams in the LHC from the CERN Control Centre (Image: CERN, from the 2011 lead-ion run).

The Large Hadron Collider (LHC) resumed operating in "stable beams" mode at 00:38 CEST on 5 April, and is rapidly coming back up to speed. The LHC experiments need stable beams to collect data for physics analysis.

In its first 6 days of operation this year, the LHC has already reached a total integrated luminosity of 0.2 inverse femtobarns – a measure of accelerator performance equivalent to about 20 trillion collisions delivered to the experiments. Last year the LHC took six weeks achieve the same number.

The number of proton bunches in the machine – currently 624 per beam - will be increased over the coming two weeks, to 840, then 1092, and finally to 1380 bunches per beam, the machine's maximum for this year. The number of protons per bunch is also increasing.

LHC - CERN

This year's higher collision energy of 4 TeV per beam (compared to 3.5 TeV per beam in 2011) and the resulting higher number of collisions expected enhance the machine's discovery potential considerably, opening up new possibilities for searches for new and heavier particles. Watch this space!

Note:

1. CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a candidate for accession. Israel is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.

After 10 years of service, Envisat has stopped sending data to Earth. ESA’s mission control is working to re-establish contact with the satellite.

Although this landmark mission has been in orbit twice as long as it was designed for, ESA hopes to keep the satellite in service until the launch of the successor Sentinel missions.

MERIS image before loss of contact

The first sign that there was a problem came on 8 April when contact with the satellite was unexpectedly lost, preventing the reception of any data as it passed over the Kiruna ground station in Sweden.

ESA’s mission control team declared a spacecraft emergency and immediately called for support from additional ESA tracking stations around the world. A team of operations and flight dynamics specialists and engineers was quickly assembled.

In a concerted effort, the recovery team, which included experts from industry, spent the next days trying to re-establish communications with the satellite.

ENVISAT in orbit

While it is known that Envisat remains in a stable orbit around Earth, efforts to resume contact with the satellite have, so far, not been successful.

As is standard practice, an anomaly review board is investigating the cause for the break in communications.

Envisat has exceeded its planned life of five years by far. Since it was launched in 2002, this remarkable satellite has orbited Earth more than 50 000 times delivering thousands of images and a wealth of data to study and understand our changing planet, establishing itself as a landmark success in observing Earth from space.

ASAR image before loss of contact

As the world’s most complex Earth observation satellite, Envisat carries 10 sophisticated instruments that have provided key information about our land, oceans, ice and atmosphere. Combined with data from the ERS missions since 1991, Envisat has provided precise measurements on climate change over the last 20 years.

More than 4000 projects in over 70 countries have been supported with Envisat data. Data in the archives will continue to be available for users.

A contingency agreement with the Canadian Space Agency on Radarsat will be activated in order to continue to serve some of the user requirements if the problem with Envisat persists.

ENVISAT description

Volker Liebig, ESA’s Director of Earth Observation Programmes, said, “The interruption of the Envisat service shows that the launch of the GMES Sentinel satellites, which are planned to replace Envisat, becomes urgent.”

The first of the new series of Sentinel missions for Europe’s Global Monitoring for Environment and Security programme is ready for launch next year.

The Sentinels will provide the data needed for information services to improve the management of the environment, understand and mitigate the effects of climate change and ensure civil security.

mercredi 11 avril 2012

ESA’s Herschel Space Observatory has studied the dusty belt around the nearby star Fomalhaut. The dust appears to be coming from collisions that destroy up to thousands of icy comets every day.

Fomalhaut is a young star, just a few hundred million years old, and twice as massive as the Sun. Its dust belt was discovered in the 1980s by the IRAS satellite, but Herschel’s new images of the belt show it in much more detail at far-infrared wavelengths than ever before.

Bram Acke, at the University of Leuven in Belgium, and colleagues analysed the Herschel observations and found the dust temperatures in the belt to be between –230 and –170ºC. However, because Fomalhaut is slightly off-centre and closer to the southern side of the belt, the southern side is warmer and brighter than the northern side.

Both the narrowness and asymmetry of the belt are thought to be due to the gravity of a possible planet in orbit around the star, as suggested by earlier Hubble Space Telescope images.

The Herschel data show that the dust in the belt has the thermal properties of small solid particles, with sizes of only a few millionths of a metre across.

But this created a paradox because the Hubble Space Telescope observations suggested solid grains more than ten times larger.

Those observations collected starlight scattering off the grains in the belt and showed it to be very faint at Hubble’s visible wavelengths, suggesting that the dust particles are relatively large. But that appears to be incompatible with the temperature of the belt as measured by Herschel in the far-infrared.

To resolve the paradox, Dr Acke and colleagues suggest that the dust grains must be large fluffy aggregates, similar to dust particles released from comets in our own Solar System.

These would have both the correct thermal and scattering properties. However, this leads to another problem.

The bright starlight from Fomalhaut should blow small dust particles out of the belt very rapidly, yet such grains appear to remain abundant there.

The only way to overcome this contradiction is to resupply the belt through continuous collisions between larger objects in orbit around Fomalhaut, creating new dust.

To sustain the belt, the rate of collisions must be impressive: each day, the equivalent of either two 10 km-sized comets or 2000 1 km-sized comets must be completely crushed into small fluffy, dust particles.

“I was really surprised,” says Dr Acke, “To me this was an extremely large number.”

To keep the collision rate so high, there must be between 260 billion and 83 trillion comets in the belt, depending on their size. Our own Solar System has a similar number of comets in its Oort Cloud, which formed from objects scattered from a disc surrounding the Sun when it was as young as Fomalhaut.

mardi 10 avril 2012

Baby stars are creating chaos 1,500 light-years away in the cosmic cloud of the Orion Nebula. Four massive stars make up the bright yellow area in the center of this false-color image for NASA's Spitzer Space Telescope. Green indicates hydrogen and sulfur gas in the nebula, which is a cocoon of gas and dust. Red and orange indicate carbon-rich molecules. Infant stars appear as yellow dots embedded in the nebula.

lundi 9 avril 2012

On 5 April 2012. At 0:38 CET, the LHC shift crew declared ‘stable beams’ as two 4 TeV proton beams were brought into collision at the LHC’s four interaction points. This signals the start of physics data taking by the LHC experiments for 2012. The collision energy of 8 TeV is a new world record, and increases the machine’s discovery potential considerably.

“The experience of two good years of running at 3.5 TeV per beam gave us the confidence to increase the energy for this year without any significant risk to the machine,” explained CERN1’s Director for Accelerators and Technology, Steve Myers. “Now it’s over to the experiments to make the best of the increased discovery potential we’re delivering them!”

Although the increase in collision energy is relatively modest, it translates to an increased discovery potential that can be several times higher for certain hypothetical particles. Some such particles, for example those predicted by supersymmetry, would be produced much more copiously at the higher energy. Supersymetry is a theory in particle physics that goes beyond the current Standard Model, and could account for the dark matter of the Universe.

Standard Model Higgs particles, if they exist, will also be produced more copiously at 8 TeV than at 7 TeV, but background processes that mimic the Higgs signal will also increase. That means that the full year’s running will still be necessary to convert the tantalising hints seen in 2011 into a discovery, or to rule out the Standard Model Higgs particle altogether.

“The increase in energy is all about maximising the discovery potential of the LHC,” said CERN Research Director Sergio Bertolucci. “And in that respect, 2012 looks set to be a vintage year for particle physics.”

The LHC is now scheduled to run until the end of 2012, when it will go into its first long shutdown in preparation for running at an energy of 6.5 TeV per beam as of late 2014, with the ultimate goal of ramping up to the full design energy of 7 TeV.

Note:

1. CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a candidate for accession. Israel is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.

The changes of a coronal cell region as solar rotation carries it across the solar disk as seen with NASA's STEREO-B spacecraft. The camera is fixed on the region (panning with it) and shows the plumes changing to cells and back to plumes again -- based on the observatory's perspective -- during the interval June 7-14, 2011. Credit: NASA/STEREO/NRL.

One day in the fall of 2011, Neil Sheeley, a solar scientist at the Naval Research Laboratory in Washington, D.C., did what he always does – look through the daily images of the sun from NASA's Solar Dynamics Observatory (SDO).

But on this day he saw something he'd never noticed before: a pattern of cells with bright centers and dark boundaries occurring in the sun's atmosphere, the corona. These cells looked somewhat like a cell pattern that occurs on the sun's surface -- similar to the bubbles that rise to the top of boiling water -- but it was a surprise to find this pattern higher up in the corona, which is normally dominated by bright loops and dark coronal holes.

Sheeley discussed the images with his Naval Research Laboratory colleague Harry Warren, and together they set out to learn more about the cells. Their search included observations from a fleet of NASA spacecraft called the Heliophysics System Observatory that provided separate viewpoints from different places around the sun. They describe the properties of these previously unreported solar features, dubbed "coronal cells," in a paper published online in The Astrophysical Journal on March 20, 2012 that will appear in print on April 10.

The coronal cells occur in areas between coronal holes – colder and less dense areas of the corona seen as dark regions in images -- and "filament channels" which mark the boundaries between sections of upward-pointing magnetic fields and downward-pointing ones. Understanding how these cells evolve can provide clues as to the changing magnetic fields at the boundaries of coronal holes and how they affect the steady emission of solar material known as the solar wind streaming from these holes.

"We think the coronal cells look like flames shooting up, like candles on a birthday cake," says Sheeley. "When you see them from the side, they look like flames. When you look at them straight down they look like cells. And we had a great way of checking this out, because we could look at them from the top and from the side at the same time using observations from SDO, STEREO-A, and STEREO-B."

The locations of STEREO–A, STEREO–B and SDO relative to the sun and Earth in 2011. Credit: NRL.

When the cells were discovered in the fall of 2011, the SDO and the two STEREO (short for Solar Terrestrial Relations Observatory) spacecraft each had widely different views of the sun. Thus, as the 27-day solar rotation carried the coronal cells across the face of the sun, they appeared first in STEREO-B data, then in SDO, and finally in STEREO-A, before starting over again in STEREO-B. In addition, when one observatory looked down directly on the cells, another observatory could see them from the side.

The researchers used time-lapse sequences obtained from the three satellites to track these cells around the sun. When an observatory looked down on one of these areas, it showed the cell pattern that Sheeley first noticed. But when the same region was viewed obliquely, it showed plumes leaning off to one side. Taken together, these two-dimensional images reveal the three-dimensional nature of the cells as columns of solar material extending upward through the sun's atmosphere, like giant pillars of gas.

To round out the picture even further, the team turned to other instruments and spacecraft. The original SDO images were from its Atmospheric Imaging Assembly, which takes conventional images of the sun. Another instrument on SDO, the Helioseismic and Magnetic Imager (HMI), provides magnetic maps of the sun. The scientists superimposed conventional images of the cells with HMI magnetic field images to determine the placement of the coronal cells relative to the complex magnetic fields of the sun's surface.

First of all, the magnetic field bundles lay centered inside the cells. This represents a clear distinction between the coronal cells and another well-known phenomenon known as supergranules. Supergranules also appear as a large cell-like pattern on the sun's surface, and their delineated edges are created as the sideways motion of solar material sweeps weaker magnetic fields toward their boundaries. Supergranules, therefore, appear to have enhanced magnetic fields at their edges, while the coronal cells show them at their centers.

Second, the scientists learned more about how the coronal cells were related to other structures on the sun, in their location between a coronal hole and a nearby filament channel. The cells consistently occurred in areas dominated by magnetic fields that point in a single direction, either up or down. In addition, the fields of the nearby coronal hole are what's known as "open," extending far into space without returning to the sun. On the other hand, the field lines in the cells were "closed," looping up over the filament channel and connecting back down to the sun.

The top images show coronal cells as viewed from above by STEREO-B (on the left) and SDO (on the right). Their diameters are about 18,000 miles. The bottom images show the same region as viewed almost simultaneously from the sides by STEREO-B (on the left) and SDO (on the right). The bottom views show the plumes as if they were leaning away from each observatory, the way a giant pillar would look if seen from the side. The heads of the black and white arrows mark identical points on the sun as seen from STEREO-B and SDO, respectively. Credit: NASA/STEREO/SDO/NRL.

The side-by-side nature of these open and closed magnetic fields – open in the coronal holes, and closed in the coronal cells – led to another scientific insight. In some of the movies, a large loop of solar material called a "filament" erupted from the adjacent filament channel. The coronal cells, with their closed field lines, disappeared and were replaced with a dark coronal hole and its associated open field lines.

"Sometimes the cells were gone forever, and sometimes they would reappear exactly as they were," says Sheeley. "So this means we need to figure out what's blowing out the candles on the birthday cake and re-lighting them. It's possible that this coronal cell structure is the same structure that exists inside the coronal holes – but they're visible to us when the magnetic fields are closed, and not visible when the magnetic fields are open."

It has long been known that isolated plumes occur intermittently inside coronal holes when very small active regions erupt there. Presumably, these eruptions are providing glimpses of discrete coronal structures similar to the more permanently visible candles adjacent to the holes. When a portion of a hole closes, the candle-like structure is suddenly lit up by the appearance of cells.

In addition to SDO and STEREO, the team went back to historical data on ESA's and NASA's Solar and Heliospheric Observatory (SOHO), which has provided observations since the previous sunspot minimum in 1996. They did not find coronal cells in 1996 or in the years around the recent sunspot minimum in 2008-2009, but they did find numerous examples of cells in the years around the intervening sunspot maximum in 2000. The recent increase in sunspot activity together with the improved observations from STEREO and SDO may explain why the cells were discovered in 2011.

The team also constructed Doppler images – images that show how quickly and where solar material in the sun's atmosphere moves toward the viewer – of the coronal cells using the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode spacecraft. These images show that the centers of the cells move upward faster than their boundaries, further rounding out the physical image of these giant candles with a section rising from the middle.

"One of the wonderful things about SDO is the way the observations can be combined with other instruments," says Dean Pesnell, SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. " Combining data from SDO, STEREO, SOHO, and Hinode lets us paint a picture of the whole sun in ways that one instrument can't."

The discovery of coronal cells has already increased our knowledge of the magnetic structure of the sun's corona. In the future, studies of the evolution of coronal cells may improve scientists' understanding of the magnetic changes at coronal-hole boundaries and their effects on the solar wind and Earth's space weather.